Principles of Beer Carbonation
The time required to reach a desired carbon dioxide concentration depends on a number of physical factors. Temperature and pressure play an important role in determining the equilibrium concentration of carbon dioxide in solution. Increasing the pressure leads to a linear increase in carbon dioxide solubility in beer. Decreasing the temperature gives a nonlinear increase in carbon dioxide solubility in beer. Consequently, the equilibrium concentration cannot be attained without either increasing the pressure or decreasing the temperature. The amount of carbon dioxide that dissolves is a function of time, with the rate decreasing exponentially as equilibrium is approached.
Pressure and Temperature
The carbon dioxide is readily soluble in the beer. According to Henry’s law, at a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. So, in an enclosed vessel such brewery tank the amount of carbon dioxide dissolved in the beer will vary according to the temperature of the beer and the pressure of the carbon dioxide in the headspace. Increasing pressure will lead to a linear increase in the weight of carbon dioxide dissolving in the beer. An increase in temperature will give a non-linear decrease in the amount of gas dissolved.
Carbon Dioxide Units
In North America, carbon dioxide solubility in beer is usually measured in volumes of carbon dioxide per volume of beer (volumes of CO2 = liters CO2/L beer) at standard temperature and pressure. One volume of carbon dioxide is equal to one liter of carbon dioxide dissolved in one liter of liquid, two volumes is equal to two liters of gas in one liter of liquid, etc.
Carbon Dioxide Levels in Beer
Typically, American lagers require carbon dioxide levels ranging from 2.45 to 2.85 volumes of carbon dioxide, while Continental lagers require carbon dioxide levels between 2.4 and 2.5. British ales with a high hop profile require carbon dioxide levels ranging from 2.2 to 2.4 volumes, and German Weiss beers have levels more than 4.0 volumes. Cask-conditioned ales have extremely low carbonation levels, typically between 1.0 and 1.5 volumes of carbon dioxide.
Carbon Dioxide Volume Table
Fixing the temperature and pressure at appropriate settings will bring about the desired carbon dioxide concentration. This relationship between pressure, temperature, and carbon dioxide volumes can be found in Appendix E, Carbon Dioxide Volume Table. To use this carbonation chart, look up the volume of carbon dioxide that is needed to dissolve in the beer, cross reference it to the temperature of the beer, and this will indicate the gas pressure needed.
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